Conventional cruise control systems control vehicle speed to an operator set speed. Adaptive cruise control systems are known which have varying degrees of interaction with preceding vehicles. A general objective of adaptive cruise control systems is to sense in path objects such as preceding vehicles and to provide throttle control to maintain a predetermined distance therefrom. Such base systems are characterized by passive deceleration, that is to say deceleration effectuated during closed throttle coast.
An exemplary adaptive cruise control system employing active vehicle deceleration, that is to say deceleration effectuated by active, controlled application of the vehicle service brakes, is disclosed in U.S. Pat. No. 5,173,859 to Deering, hereafter "Deering", also assigned to the assignee of the present invention. Deering describes a system wherein vehicle braking control is invoked to decelerate a succeeding vehicle when the succeeding vehicle violates a predetermined range from the preceding vehicle with a range rate indicating that the succeeding vehicle is closing on a preceding vehicle.
In Deering, the determination of a desired succeeding vehicle deceleration is in accordance with coincidental occurrence of a predetermined desired minimum inter-vehicle spacing or range, and convergence of the respective vehicle velocities. Deering operates with the assumption that the preceding vehicle deceleration is adequately accounted for through the relative deceleration expressed implicitly in iterative updates to range rate information. Under certain driving conditions, for example during city driving conditions, the implicit accounting for preceding vehicle deceleration may result in deceleration determinations insufficient to meet certain objectives of the system, for example a minimum separation distance objective. Explicit inclusion of preceding vehicle deceleration into the determination of the desired succeeding vehicle deceleration, still in accordance with coincidental occurrence of the predetermined minimum desired range and convergence of the respective vehicle velocities, provides for improved succeeding vehicle deceleration determinations. However, such inclusion of preceding vehicle deceleration in determining the desired succeeding vehicle deceleration may have the undesirable effect of producing succeeding vehicle deceleration which may be unnecessarily too aggressive resulting in inefficient inter-vehicle spacing during preceding and succeeding vehicle decelerations.